1. Field of the Invention
The present invention relates to a method for measuring simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant and the apparatus therefor, and more particularly to a method for measuring simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant by which an absolute molecular orientation can be calculated simultaneously with an effective second order nonlinear optical constant without changing its measuring system as well as the apparatus therefor.
It is to be noted herein that the term xe2x80x9cabsolute molecular orientationxe2x80x9d means xe2x80x9cdirection (direction in vector) of polar molecular alignmentxe2x80x9d.
2. Description of the Related Art
It is recognized in general to obtain a higher second order nonlinear optical response with use of a polymer material is one of important problems in realizing an optical active element by the use of a polymer element.
In order to achieve such problem, development for a molecule having a high primary polarizability is important as a matter of course, besides it becomes also an important problem to increase a degree of molecular orientation in a medium by what kind of manner, and to obtain stable molecular orientation by what kind of manner.
Under the circumstances, it is considered that molecular orientation, i.e., generation of molecular polar alignment is influenced by molecules and a surrounding atmosphere of the molecules.
In order that a mechanism for such generation of molecular orientation is elucidated to obtain a higher degree of molecular orientation in a medium as well as to obtain a more stable molecular orientation, it is important to correctly grasp the molecular orientation in the medium.
Meanwhile, for example, a second harmonic generation phase method (hereinafter referred optionally to as xe2x80x9cSHG phase methodxe2x80x9d) has been known as a conventional manner for measuring a molecular orientation in a medium.
In the SHG phase method, it is arranged in such that a fringe obtained from an object to be measured having an unknown absolute molecular orientation is compared with a fringe obtained from a material having a known absolute molecular orientation to determine the absolute molecular orientation in the object to be measured.
On one hand, as a method for determining an effective second order nonlinear optical constant in a medium in response to a absolute molecular orientation in the medium, for example, Maker fringe method has been known.
In this respect, however, according to a conventional technique wherein an absolute molecular orientation in a medium is determined by the above described SHG phase method, while an effective second order nonlinear optical constant in response to an absolute molecular orientation in a medium is determined by the above described Maker fringe method, since a measuring system of the SHG phase method differs from that of the Maker fringe method, there has been such a problem that the absolute molecular orientation cannot be calculated simultaneously with the effective second order nonlinear optical constant in respect to the same measuring point of the same object to be measured.
Furthermore, according to the above described conventional technique, there have been also such problems that a long period of time is required for measuring an absolute molecular orientation as well as for measuring an effective second order nonlinear optical constant in an object to be measured, because measurement in SHG phase method in a measuring system as well as measurement in Maker fringe method in another measuring system are must be separately carried out, and that there is a tendency of damaging the object to be measured.
The present invention has been made in view of a variety of the above described problems involved in the prior art, so that an object of the invention is to provide a method for measuring simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant as well as an apparatus therefor by which the absolute molecular orientation can be simultaneously calculated with the effective second order nonlinear optical constant in an object to be measured without changing its measuring point.
Moreover, another object of the present invention is to provide a method for measuring simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant as well as an apparatus therefor by which a period of time for measuring the absolute molecular orientation and the effective second order nonlinear optical constant in an object to be measured can be reduced, and at the same time, a possibility of damaging the object to be measured can be minimized.
In order to achieve the above described objects, the present invention has been constituted in such that measurement is conducted by the use of a single light source in accordance with SHG phase method without shifting a measuring point of an object to be measured, a fringe attained by the measurement is subjected to fitting to obtain a fitting curve, and an absolute molecular orientation and an effective second order nonlinear optical constant are calculated from the fitting curve.
Accordingly, as a result of single measurement according to SHG phase method, an absolute molecular orientation and an effective second order nonlinear optical constant in an object to be measured can be calculated at the same time without changing a measuring point thereof in accordance with the present invention.
Furthermore, according to the present invention, since it is sufficient for conducting only single measurement of SHG phase method, a period of time required for measuring an absolute molecular orientation and an effective second order nonlinear optical constant in an object to be measured can be reduced so that a possibility of damaging the object to be measured can be minimized.
Namely, the present invention comprises a first step for obtaining a fringe as to an object to be measured by the use of a measuring reference sample in accordance with second harmonic generation phase method wherein a single light source is used; and a second step for fitting the fringe obtained in the above described first step to obtain an effective second order nonlinear optical constant and at the same time, to obtain an absolute molecular orientation on the basis of a sign of the effective second order nonlinear optical constant.
In this case, the fitting in the above described second step may conduct fitting of the fringe in such a manner that known values are substituted for an operation expression representing a power of second harmonics at the position where second harmonics generated from the measuring reference sample in accordance with the second harmonic generation phase method interfere with other second harmonics generated from the object to be measured thereby changing fitting parameters.
Moreover, the present invention relates to a measuring apparatus of the type containing a light source as well as a measuring reference sample, a phase generator, and an object to be measured which are successively disposed on an optical path of the above described light source, and obtaining a fringe as to the object to be measured by the use of the measuring reference sample in accordance with second harmonic generation phase method, comprising a fitting means for, fitting a fringe as to the object to be measured; and an acquiring means for obtaining an effective second order nonlinear optical constant on the basis of the fitting by the above described fitting means and at the same time, obtaining an absolute molecular orientation based on a sign of the effective second order nonlinear optical constant.
In this case, the above described fitting means may conduct fitting of the fringe in such a manner that known values are substituted for an operation expression representing a power of second harmonics at the position where second harmonics generated from the measuring reference sample in accordance with the above described second harmonic generation phase method interfere with other second harmonics generated from the object to be measured thereby changing fitting parameters.
Still further, the present invention relates to a recording medium readable by a computer, constituted in such that a program for executing by the computer the method for measuring simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant of the invention as described above is stored therein.